This invention relates generally to medical devices and more particularly, to needles that are curved for indirect infusion access within the body.
Medical procedures involving the vertebrae are typically complicated because of the preciseness required to avoid both neural damage and injury to major blood vessels, as well as the indirect path that is usually required to access the treatment site. This is certainly the case when performing a vertebroplasty, a procedure whereby bone cement, most commonly methyl methacrylate, is injected into a vertebral body to provide stabilization and/or pain relief in selected patients having a spinal condition such as osteolytic metastasis and myeloma, painful or aggressive hemangioma (benign lesions of the spine), or painful osteoporotic vertebral collapse. Standard treatment practice depends on the region of the spine being treated. For the cervical vertebrae, anterolateral access is used with a 15 gauge needle. The large vessels adjacent to the vertebra are laterally manipulated by the radiologist to provide an access site between the vessels and the pharyngolarynx. An upward access route is required because the needle must be introduced below the mandible. When accessing the thoracic or lumbar vertebrae, typically a large 10 gauge needle is used following a transpedicular or posterolateral approach. The transpedicular route is preferred to avoid spinal nerve injury and to decrease the probability of the cement leaking out into tissues adjacent to the vertebral body. To obtain a complete filling of a damaged vertebral body, it is often required that a second transpedicular access be made from the opposite side. A single infusion usually cannot fill the entire target area because the needle tip cannot be redirected from the original plane of entry. Continued infusion of cement from the first access site will usually not result in an adequate infusion due to the tendency of the material to set before it fills all of the affected area, thereby becoming a barrier to itself. Furthermore, the thick density of the marrow and structures, such as veins, usually acts to impede free flow of the cement within the vertebral body. Another concern during the procedure is accidental puncture of the these veins. Because vertebral veins lead directly to the lungs, there is a significant risk of pulmonary embolism if cement is accidentally introduced therein.
The inability to adequately maneuver the needle cannula tip within a body or around structures is a major limitation of the straight needle. Additional needle sticks to complete a medical procedure provide discomfort to the patient and additional risk of leakage and other complications. In order to sufficiently access a vertebral body for complete infusion of cement, the tip must be able to be deflected at significantly large angles from the original axis. This would require that the needle have a distal bend so that it could be rotated to selectively direct the material. Rigid curved needles are well known for suturing applications; however, adding anything more than a slight bend to an infusion needle limits its access path and ability to deeply penetrate tissue, especially bone. For example, a rigid curved needle would be unsuitable for use in a vertebroplasty procedure where the needle cannula must be driven through the bone and deep into the vertebral body using a relatively straight approach and maintained in place to avoid additional damage to the entry site. While the initial access must be done with a straight needle of sufficient strength to penetrate bone, the ideal approach would be to be able to direct a lateral infusion of cement following penetration, and then to withdraw the needle along its original path. Accomplishing this is problematic in that the density and resistance of the tissue at the treatment site can require that the inner infusion member be nearly as stiff as the outer piercing cannula. A certain degree of rigidity is required to be able to maneuver the inner member and accurately direct the flow of material. While stainless steel infusion needles having a slight distal bend are known, the amount of curvature necessary to provide adequate lateral infusion would not be possible in that the needle would be plastically deformed once inside the outer restraining cannula and be unable to resiliently return to its preformed shape. Thus, a second needle access would still be required to provide adequate filling.
Other medical procedures provide similar problems when a single straight needle is used. One example is tumor ablation where percutaneous ethanol injection is used to treat carcinoma of the liver and kidney. Originally introduced as a palliative treatment for inoperable hepatocellular carcinoma of the liver, ethanol injection has now been shown to have curative potential comparable to resection in many patients, especially for smaller tumors. Current practice has been to directly inject ethanol into masses using a straight needle and allow the ethanol to infuse from one or more side holes into the tissue. The problem is that the infusion may not penetrate any deeper than the needle tract and thus, portions of the tumor are not effectively treated. It is desired to provide a device for more effective infusion of ethanol into the tumor mass.
The foregoing problems are also solved and a technical advance is achieved in a curved member, such as a medical needle for use for example for infusion or aspiration, and made of a rigid superelastic material and having at least one preformed bend along the distal portion of its length. The needle is used coaxially with a second hollow cannula for restraining the needle in a substantially straight orientation during percutaneous introduction to the target site, whereby the needle is deployed to resiliently return to its preformed configuration. The ability of the preformed needle to deflect laterally upon exiting the restraining allows it to infuse or aspirate material at multiple points within different planes in the body by rotating the needle about its longitudinal axis. This is important in helping to reduce or eliminate the need for additional xe2x80x9csticksxe2x80x9d with the outer cannula. It also allows the operator to make an entry from one direction, then to deploy the curved to reach a site that cannot be accessed directly, such as where another structure lies along the access path, thereby blocking the target site.
The preferred material for the needle is a superelastic, shape memory alloy such as nitinol (Nixe2x80x94Ti); however, there are other non Nixe2x80x94Ti alloys that may be used. A nitinol alloy is selected that has properties whereby the temperature at which the martensitic to austenitic phase change occurs is lower than the working temperature of the device (i.e., room temperature). As described by Jervis in U.S. Pat. No. 5,597,378 filed Oct. 2, 1992 and incorporated herein by reference, a permanent bend may be heat set in a superelastic nitinol cannula by maintaining the cannula in the desired final shape while subjecting it to a prescribed high temperature for a specific time period. The cannula can be elastically manipulated far beyond the point at which stainless steel or other metals would experience plastic deformation. Nitinol and other superelastic materials, when sufficiently deformed, undergo a local phase change at the point of stress to what is called xe2x80x9cstress-induced martensitexe2x80x9d (SIM). When the stress is released, the material resiliently returns to the austenitic state.
A second method of imparting a permanent bend to the material is by a process commonly known as cold working. Cold working involves mechanically overstressing or overbending the superelastic cannula. The material within the bending region undergoes a localized phase shift from austenite to martensite and does not fully return to its original shape. In the case of the cold-worked cannula, the result is a permanent curve about the bending zone which has been locked in to at least a partial martensitic crystalline state. In contrast, the entire heat-annealed cannula is in a austenitic condition, even in the curved region, and only is temporarily transformed to martensite under sufficient bending stresses. Therefore, the flexural properties of the annealed cannula vary little across its length. Conversely, the bend of cold-worked cannula, which contains martensite, has increased resistance to deformation and therefore, holds its shape better than the more flexible bend of the pure austenitic cannula. This increased rigidity can be an advantage for certain clinical applications.
In a first embodiment of the invention suitable for many clinical applications involving infusion, an introducer trocar or stylet are used with either a restraining cannula or needle cannula there within depending on the luminal size of the needle, to facilitate access of tissue and/or prevent coring tissue into the distal tip of the device. The infusion needle cannula is introduced through the outer restraining cannula after access has been established and the trocar or stylet is removed. Depending on the size of the cannulae, the degree of the preformed bend, or the method used to form the bend, the inner cannula may slightly deform the outer cannula as the preformed bend is constrained within the outer cannula. As a result, the outer cannula may be deflected a few degrees from its normal longitudinal axis at a point corresponding to the bend of the inner cannula. As the inner cannula is deployed from the outer cannula, it deflects laterally until the entire region of the bend is unsheathed. In the preferred embodiments the distal opening of the inner cannula is oriented at a large angle (preferably within the range of 60-90xc2x0) from the original longitudinal axis when the inner needle is fully deployed.
The ability of the inner cannula to deflect at a significant angle from the original longitudinal axis has great utility in a number of applications where straight access is required followed by redirection of the distal opening. This permits access to a different site without the necessity of withdrawing and reintroducing the needle. A primary example of such a procedure is vertebroplasty in which infusion of the stabilizing cement with a conventional straight needle often requires a second stick to provide a complete filling to stabilize the vertebral body while avoiding damage to delicate structures such as veins. As with the standard single-needle procedure involving the thoracic or lumbar regions of the spine, a transpedicular approach is normally used whereby the larger outer needle cannula, such as a coaxial Jamshidi-type needle, is introduced into the damaged or diseased vertebral body. The outer needle includes an inner introducer trocar which is then replaced with a inner curved needle for infusion of the cement. The ability of the curved needle to self-deflect laterally and rotated to reach multiple planes, gives it a significant advantages over straight needles which have a limited range of infusion. Because of this additional range of movement, the curved needle of the present invention can usually complete the vertebroplasty procedure with a single access or stick of the vertebral body. This avoids additional discomfort and risks to the patient, which include complications from leakage of cement or inadvertent infusion into non-target areas.
In addition to using the coaxial needle for infusion of cement in the above embodiment, the device can also be adapted for aspirating material or serving as a conduit for the introduction of other devices. It is contemplated that the present invention can be used for a percutaneous corpectomy, a procedure which involves fusion and decompression of two or more vertebrae by first aspirating tissue from the damaged vertebral bodies, then introducing a carbon fiber composite cage packed with bone graft material to serve as scaffolding for the affected vertebrae. Once the cage is properly positioned, methyl methacrylate or another suitable material is infused into the vertebral bodies to secure the prosthesis. The percutaneous corpectomy offers less trauma and with the reinforcement cage, provides superior rigidity over a conventional corpectomy utilizing bone graft material alone.
In another aspect of the invention, the coaxial needle can be adapted for paraspinal use to inject medicaments within the neural canal or epidural space as part as management and/or diagnosis of pain. Preferably, the outer cannula has a tip adapted for piercing soft tissue. This outer needle cannula, preferably about 21 gauge, is introduced percutaneously parallel to the spinal column along with an internal stylet with matched bevel to prevent the curing of tissue into the distal opening. The stylet is removed and the curved needle, about 25 gauge, is inserted into the outer cannula. The needle assembly is then maneuvered to contact a nerve root during a diagnostic procedure to help recreate pain symptoms of the patient. The inner infusion needle also includes a stylet which is situated within the passageway of the needle as it is directed to the target site. The stylet is then removed from the infusion needle and medicaments, commonly steroids such as Celestone (injected with lidocaine), Kenalog, or methylprednisone are introduced to the treatment site. The inner needle is then withdrawn into the outer sheath cannula and both are withdrawn from the patient.
Another use of the smaller gauge paraspinal needle is for diskography procedure. Diskography consists of injecting a contrast agent (preferably nonionic contrast media) directly into the disk to delineate the extent of any malformations or injury to the vertebral body.
Yet another embodiment of the invention solves the problem of infusion of ethanol into a tumor mass by utilizing a plurality of curved needle cannulae that can be deployed within an introducer cannula into the tumor where they radiate outward into an umbrella-shaped configuration. Therefore, infusion can take place at multiple points within the tumor to provide wider dispersion of the ethanol. Following treatment, the needle cannulae are withdrawn into the cannula and the device is removed from the patient.
In a related embodiment, one or more needle cannulae are located proximal to the distal end of the infusion needle. These proximally-located cannulae allow infusion of medicaments at different points along the length of the device. By having multiple sets of needles arranged in the umbrella configuration, the volume of tissue treated is increased. The coaxial outer cannula includes a plurality of side apertures that allow the proximally-located needle cannulae to deploy after the infusion needle is placed at the desired location in the body and the outer cannula is withdrawn. An outer sheath over the coaxial outer cannula selectively exposes the side apertures to permit the appropriate alignment of needle cannulae and apertures when there are multiple rows of each.